Composite materials of metals and reinforcing silicon carbide fibers potentially possess high toughness levels and good performance characteristics, thereby making them highly suitable for applications which require light-weight structural materials having high elasticity, high strength, shapability, heat stability, electrical conductivity and heat conductivity. These composites are being increasingly investigated for structural applications.
It is known that many fiber-matrix combinations undergo extensive chemical reaction or interdiffusion between the fiber and matrix materials, each of which is likely chosen for the contribution of specific mechanical and/or physical properties to the resulting composite. Such reaction or interdiffusion can lead to serious degradation in strength, toughness and temperature stability. The fiber-matrix interface is therefore very important to preventing or minimizing chemical reactions and interdiffusion.
Surface modification of the fibers is an effective means to control the fiber-matrix interface. This can be accomplished by coating the fibers with a suitable composition to inhibit the fibers from reacting or bonding with the matrix.
A variety of coatings have been proposed for SiC reinforcements intended for use in fiber-matrix composites. U.S. Pat. No. 3,717,443 describes a composite having zirconium coated SiC reinforcing filaments in a titanium or titanium alloy matrix. Zirconium is disclosed as acting as a barrier to interdiffusion of titanium and SiC and prevents weakening of the composite structure.
U.S. Pat. No. 3,556,836 discloses a boron filament having a thin protective layer of SiC and an overcoat of a matrix material including metals such as aluminum, magnesium, titanium, and alloys thereof.
U.S. Pat. No. 3,811,920 discloses the use of silicon carbide surfaced filaments such as filaments of SiC, SiC coated boron and SiC coated carbon which are coated with a thin layer of titanium carbide. These coated filaments are used in metal matrix materials such as titanium and nickel.
U.S. Pat. No. 4,132,828 discloses an assembly of a plurality of carbon fibers incorporated into a metal matrix of Al, Ti, Mg, Zn, Pb, Sn, Ni, Fe, Co, Cu, Ag or Au. The metal matrix containing carbon fibers may also include a layer of titanium or silicon or a carbide or nitride thereof coated on the carbon fibers.
Composite materials containing fibers which are coated to prevent or minimize interdiffusion between the fiber and matrix maerial are often excluded from high temperature applications because of concerns regarding the thermomechanical stability, thermochemical stability, and high temperature fatigue resistance encountered in atmospheric conditions at temperature above 1000.degree. C.
Accordingly, an object of the present invention is to provide a coating for silicon carbide reinforcements which permits the use of the reinforcement in titanium and titanium alloy matrix materials for use at temperatures above 1000.degree. C.
Another object of the invention is to provide a coating for silicon carbide reinforcements which prevents chemical reaction between the fiber and the matrix.